Excavations at two quarries in Wales suggest that Stonehenge’s famous “bluestones” were quarried around 5,000 years ago and traveled in a novel way to their final resting place 290 kilometers (180 miles) away.

The two quarries show evidence of megalith quarrying in 3000 BCE, the same period of the first state of Stonehenge’s construction. Writing in the journal Antiquity, researchers pinpoint the exact locations of two of Stonehenge’s stone sources, further suggesting that the large stone pillars were excavated using a sophisticated wedging system and later transported by moveable platforms to a temporary spot near Stonehenge’s current location in Wiltshire, southwest England.

“What's really exciting about these discoveries is that they take us a step closer to unlocking Stonehenge's greatest mystery – why its stones came from so far away," said study author Mike Parker Pearson in a statement.

Pembrokeshire in western Wales is home to the largest quarry contributing to Stonehenge, found on the outcrop of Carn Goedog on the north slope of the Preseli Hills – nearly 300 kilometers away from the megalith. It’s here that 42 of Stonehenge’s smaller stones, known as “bluestones”, are believed to have originated from.

"This was the dominant source of Stonehenge's spotted dolerite, so-called because it has white spots in the igneous blue rock. At least five of Stonehenge's bluestones, and probably more, came from Carn Goedog," said geologist with Richard Bevins of the National Museum of Wales.

Natural, vertical pillars that could be easily broken off by opening vertical joints between each bluestone outcrop would have made the quarrying of these stones quite easy. Neolithic workers could have inserted wedges into these joints and then simply lowered them using a man-made stone and earth platforms discovered just below the pillars.

"Bluestone pillars could be eased down onto this platform, which acted as a loading bay for lowering them onto wooden sledges before dragging them away," said researcher Colin Richards. Hammers and wedges made of stone found at the site further support this claim.

“Some people think that the bluestones were taken southwards and placed on rafts or slung between boats and then paddled up the Bristol Channel and along the Bristol Avon towards Salisbury Plain. But these quarries are on the north side of the Preseli hills so the megaliths could have simply gone overland all the way to Salisbury Plain,” said Professor Kate Welham.

The researchers believe Stonehenge was once a circle of unworked bluestone pillars set in pits near its current location before the larger sandstone blocks known as sarsens were added half-a-millennia later. But why ancient architects chose to move the massive stones such a far distance still remains a mystery.

“Every other Neolithic monument in Europe was built of megaliths brought from no more than 10 miles away. We're now looking to find out just what was so special about the Preseli hills 5,000 years ago, and whether there were any important stone circles here, built before the bluestones were moved to Stonehenge,” said Parker Pearson.